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It looks like you are using a ball end mill (has a radius on the tip). You need to either use a very small finishing stepover to reduce the height of the ridges, or use a cutter with a flat end (normal flat end mill). For this application, a flat end mill is probably the right tool for the job.

Using a V bit means you’ll have to make very small cuts to get anything close to a flat surface within those letters. A flat bit will be much better. V bits are best for carving, where there are lots and lots of small movements giving curved surfaces.